Build with liburcu, Userspace RCU

BIND needs a collection of standard lock-free data structures,
which we can find in liburcu, along with its RCU safe memory
reclamation machinery. We will use liburcu's QSBR variant instead
of the home-grown isc_qsbr.

lib/isc/Makefile.am

@@ -212,6 +212,7 @@ endif USE_ISC_RWLOCK
 libisc_la_CPPFLAGS =		\
 	$(AM_CPPFLAGS)		\
 	$(LIBISC_CFLAGS)	\
+	$(LIBURCU_CFLAGS)	\
 	$(LIBUV_CFLAGS)		\
 	$(OPENSSL_CFLAGS)	\
 	$(ZLIB_CFLAGS)
@@ -221,6 +222,7 @@ libisc_la_LDFLAGS =		\
 	-release "$(PACKAGE_VERSION)"
 
 libisc_la_LIBADD =		\
+	$(LIBURCU_LIBS)		\
 	$(LIBUV_LIBS)		\
 	$(OPENSSL_LIBS)		\
 	$(ZLIB_LIBS)